Experts are racing to contain 'the most dangerous' monkeypox virus yet before it causes a global outbreak

• A new strain of monkeypox virus is "the most dangerous" yet and could be a global threat, experts say.
• The new clade Ib virus emerged in the Democratic Republic of the Congo and spread to Rwanda's border.

A deadly and fast-spreading new strain of mpox, the disease caused by the monkeypox virus, has global health officials ringing alarm bells.

The new virus is "undoubtedly the most dangerous of all the known strains of mpox," John Claude Udahemuka, a lecturer at the University of Rwanda, said in a press briefing on June 25. He said the virus has caused miscarriages and blindness.

An earlier, milder form of mpox — called clade IIb — circulated worldwide in 2022, ultimately infecting more than 32,000 people in the US and killing 58 of them. It prompted the World Health Organization to declare a public health emergency, which ended last year.

The new virus is called clade Ib, since it's a mutation of an even earlier form of mpox. It first appeared in a remote region of the Democratic Republic of the Congo in September and has spread to towns along the Rwanda border, near Burundi and Uganda.

The new clade Ib virus could cause a global outbreak, experts fear, though they stopped short of warning of a pandemic.

"The pandemic question is difficult," Trudie Lang, director of the Global Health Network at Oxford University, said in the briefing.

"I think we need to be really vigilant now and move to try and contain this as quickly as possible in this region," she added. "There's definitely the opportunity for this to get on an airplane."

The new mpox strain spreads easily

Mpox spreads through close contact, especially skin-to-skin contact. It can cause flu-like symptoms and a painful or itchy rash that develops into puss-filled blisters, lesions, and eventually scabs.

Previous strains of the virus have had limited transmission abilities. The clade I virus that's long circulated in the DRC has been mostly associated with spread through families and within households, Land said. The clade IIb virus that went global was mostly sexually transmitted and mostly affected men who have sex with men.

The new clade Ib strain seems to do it all.

It began spreading through sexual transmission, via the local sex work industry, according to the researchers. However, they said the new virus has also spread within households, between mothers and their children, and there have even been cases of person-to-person spread outside households and without sexual contact.

That's "incredibly worrying," Lang said. That's because it has more opportunities to spread than previous strains did.

The clade I form of the virus, from which the new strain has emerged, is also more deadly than clade II. According to WHO, some outbreaks have killed up to 10% of sick people.

Researchers only see 'the tip of the iceberg'

It's not yet clear just how deadly the new clade Ib virus is, because researchers aren't sure how many cases there are.

Leandre Murhula Masirika, a research coordinator in the local DRC health department, said in the briefing that they had identified more than 600 cases so far.

"These are the severe cases that make it to hospital, so this will be the tip of the iceberg," Lang said.

The WHO's technical lead for mpox, Rosamund Lewis, also raised the alarm last week, saying "There is a critical need to address the recent surge in mpox cases in Africa," according to Reuters.

The researchers said they need to better understand the virus to identify the right safety measures and vaccines to contain its spread.

"We need to first carry out studies of serology and immunology in order to see what kind of vaccination we can propose," Murhula Masirika said.

He added that, in the meantime, he wants to give the smallpox vaccine to local sex workers and healthcare workers in hopes that it will confer some immunity to mpox.